I did it a while ago. A few times - not many. And not for a while.
No serious problem. The Viagra still works, in a way. But
(a) if your dick tends to be a bit floppy and lacklustre when pumped - as many do - then Viagra won't change that. And it may make it more difficult at some chemical level. I don't know... and ...
(b) if you get the usual side effects with Viagra ( not everyone does ) like slight indigestion or slight visual distortions, that could be worse. I think unless Viagra has a good working cock ( unimpeded by bloating / pumping ) to work on, maybe something gets sort of "left over" at a biochemical level ? I don't know, I'm just guessing ?