Gibbs
Ground-float aerials still do lead to better followups, not because you cancel lag but because you hit the ground sooner. It's a bit of a trade-off. Think of it this way: if you do a SH-nair OOS, you ideally begin the nair immediately upon leaving the ground, but odds are you won't be able to follow up with anything since Peach takes a while to get back to the ground, even with the aid of fast-falling. On the flip side, if you do a ground-float nair OOS, you'll need to jump, immediately float, and then begin the nair, which is technically slower (not by much but every frame counts in match). However, since you cancel your vertical momentum, you're on the ground immediately and can gain better ground or get a followup off of it. Different options for different situations. I main DJC characters with good punish games in PM (part of why I love Peach so much in this game) so I go over this tradeoff a lot.
So basically; if you think that you can't get a ground-float aerial out of shield fast enough (say the opponent is rushing you down and applying a good deal of pressure) then a regular short-hop nair OOS is probably the better choice because at that point you're more concerned about finding a good 'get-off-me' move to give yourself some breathing room. If you're punishing a shield poke you know is unsafe and you're confident a ground-float aerial will connect then by all means go for it. One of Peach's biggest strengths is her burst offensive options with float and deadly punish game. Make them hurt for hitting your shield wrong.
Keep in mind that most of what I said here mainly applies to nair OOS. Bair OOS won't really lead to followups regardless of whether you float or not, so to my knowledge it's generally best to SHFFL it if they've crossed up your shield and you can't get anything else. Fair OOS is probably not a very good option outside of very specific scenarios, floated or otherwise. Dair is very flexible and still has followups whether you do it out of a float or a short hop, although it probably isn't the best OOS option unless they've done something pretty unsafe on shield considering its speed and hitbox placement. Uair OOS can net different followups depending on whether or not you float it (regular uair as opposed to the initial spike hitbox) but it really only works if your opponent is big or directly above you. Nair is really the only good OOS option whose application changes significantly depending on whether you ground-float it or not.
Hope this helps! ^_^
