Depending on the type of grass, they can mat down, become impenetrable, and turn slimy underneath.

Try a small section to see how yours works, or mix the clippings with the leaves for a texture difference.

Mixing with the leaves is a good idea.

(I am asking this as I have run out of room in my 3 residential wooden composters and I was hoping I could use the fall grass clippings directly on the soon to hibernate perennial garden)

I've used grass clippings directly on the soil, sometimes topped with mulch, sometimes mixed with mulch. Grass clippings seem to break down quickly in my garden so aren't a long lasting mulch. In your zone over winter it will be a good mulch and you could top with a longer lasting mulch in the spring.

I've never had a problem with them matting, becoming impenetrable, or turning slimy underneath but different weather/zones I'm sure makes a difference.

Try it to see how it works for you. Worms love grass clippings.

I've used them in the vege garden and it seemed to warm things up early in the spring (just a guess! LOL) I made sure that there were gaps where water could get in and I kept it to about 2-4". I moved it around every few days so it didn't matt up. Nancy

I mulch the grass clippings right back into the lawn. I think that is the easiest and best way to get the benefits out of their moisture and nitrogen.

I have used grass clippings as mulch in the garden beds and found that if they are thick enough to actually be a mulch they did tend to matt and not allow water to penetrate and they smelled really bad. I have also mixed grass clippings with shredded leaves and found those problems disappeared.
By themselves they could be a problem, mixed with other materials they are quite good materials,

I mulch the grass clippings right back into the lawn.

I would if they were from my lawn but I have a neighbor who knows I compost and so he has been good enough to brings me his clippings all season. It is just now in the fall with leaves and such that I have no more room in my composters.

As long as they are not treated with herbicides, they should be OK, as long as they are not too thick.

Grass/leaves mix is ideal because the leaves help keep it fluffed up and doesn't mat down as much. Plus you get a balanced compostable mix of ingredients that way.

I use a mulching mower but in the fall I bag up the last couple of mowings which are leaf and grass mix. It either goes on the garden as a mulch/sheet compost layer, or into the compost bins.

they did tend to matt and not allow water to penetrate and they smelled really bad.

I wouldn't think either of these (water and smell) would be an issue for grass mulch used in late fall in my zone 4 i.e. there is so much precipitation this time of year and with the cold and snow soon to happen there would be no odor.

My neighbor used my yards clippings on his veggie beds. I have a mostly weed yard. I am not sure if he had weeds because he tended to his stuff pretty often during the growing season. When I get leaves and grass in bags at our compost site, any green grass mixed with the fall leaves is all grass, so it may be fertilized, bec ause it looks like manicured grass, no weeds. I try to get only fall leaves though.

Rouge, you would be surprised at how hot, and stinky, a pile of grass can get even around Thanksgiving. With a Carbon to Nitrogen ratio of about 20:1 the wee bacteria that digest those materials will get to work even of the air temperature are around freezing and generate a lot of heat which the causes ammonia, the stink, to be released.
Been there, seen that.

Quite true, for a pile, but a mulch layer a few inches thick will not be able to heat up.

I agree with Kimmsr

clippings mulched between the rows to thickly causes odor when watered heavily as the soil doesn't get a chance to breath so I spread it on thinly and apply the clippings more often to give them a week or so to dry out and start breaking down. If you have a whole bunch of clippings and leaves in the fall spread them on your garden and till them in and add water and let nature do its thing and by spring when you are preparing your garden it will be part of your soil.

Tox, I have seen grass clippings layered 3 to 4 inches thick develop quite a bit of heat and produce a very strong ammonia odor, if all that was spread was those grass clippings. If higher carbon materials are mixed in, leaves for example, that usually will not happen.

I guess I have never witnessed grass clippings laid down that thickly as a mulch, in hot weather. I always mix them with leaves myself, which keeps them aerated and balances the CN ratio. I've put down up to 6" of that as summer mulch and have not seen that happen.