Glide tossing:
With a turnip in hand and in shield, if you're suffering some shield pressure from other characters, a glide toss while moving away can get them off your back (but taking into account how far they usually get hit there isn't enough hitstun to get a conversion). The effectiveness really depends on which way you face; rolling in the direction you face means you get more distance and it's safer, but rolling in the opposite direction gets your glide toss less distance, which sucks.
If your opponent likes to approach from vertically above you, you can GT while throwing the turnip upwards. This is kind of a gimmick though and once they're onto it you can get punished pretty hard.
The only other instance I've used GT in is spacing and approaching. On one hand it's not that great for approaching because jump + throw keeps your aerial momentum while a GT does not. On the other hand it's good if being in the air is disadvantageous against your opponent. Overall, unless I'm missing something, GT is kind of overrated in PM. I might be wrong because I can't access my game right now but I believe it's shorter? Maybe I should look at the Brawl Peach boards or ask someone who probably extensively used it. @
Praxis probably knows enough about it in both games to provide his opinion on it.
Aerial glide tossing:
This is a better I think. Vertical AGT still goes very far. Sometimes against other floaties, I'll do upthrow and pluck a turnip, and then it becomes a game of me keeping them up in the air and them coming back down. If they're not really doing anything, AGT up or up-diagonally with a turnip leading the way and try to follow up with an aerial. After your opponent knows you can do this, you can mix this up with trying to bait out aerials and airdodges. Just know that a lot of characters can airdodge and get to the ground faster than Peach can, lol.
Horizontally it depends. AGT in the opposite direction is very noticeable and can be used to reverse your momentum, more easily whiff punish, etc. AGT in the direction
you face you already move in sucks, and you won't really notice a difference between that and just moving in that direction, honestly. I understand that burst movement is kind of undesirable, but I wish horizontal AGT was better.
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Against one of my training partners (a Marth), one of the only useful ways to use a turnip is to have it lead your way and attack based on what they do. He's so used to fighting me that he now AGTs turnips to aid his recovery if I throw them offstage (I don't anymore), he just wavedashes to catch them on the ground, or airdodge to catch --> AGT to throw it back to me. In Melee he just loses aerial options but in PM he can actually do stuff lol.
Now that a lot of recoveries of the previous lower cast members don't suck as much, yeah it's harder to edgeguard with them. I prefer to just grab ledge and do ledge stuff or to go out and aerial them and things like that.
I can't remember having turnips deflect my opponents towards the stage before, but I can't deny it's never happened. I don't really know what to do about that other than to tell you it sucks lol.