Yes its a bad thing lol. But I do it all the time!! Haven't learned my lesson yet but I swear this is the last run doing it. Its just so hard to pick one lol. I have a strain that was supposed to be the same finishing time as another and its now about two weeks behind so I'll have a pile of dead or dying roots in the res while I wait!! Also the height difference can be a bitch. Then there's the difference in nutritional needs for each strain. No it's a bad ideal lol.