Ya alot of experienced guys actually don't aspirate. I think it's ridiculous not to since it only takes a second and adds another layer of safety imo. So I say aspirate as well.
But effects...no I don't think any difference. I've heard some guys will do spot injections like in shoulders or calves or even pecs because they feel it can help stretch the fascia sort of similar to synthol injections, but I'm leery on buying that. Unless your injecting a large amount of gear I don't know if I buy it.
If your pinning daily I would def switch between legs and glutes never hitting the same spot every day. But that's just me