For me it depends on a few factors. As @Hilly1979 said, the opposition do play a part. For example if I'm managing Ludogorets and I'm away to PSG, there is no way I'm going to berate the team if we're losing. Morale is already going to take a hit if we lose and lose heavily. I don't want to compound it further by losing it with the players and potentially running into a poor run of form in the next few games.
New signings: If I have made a few new signings and they're in the line-up, I won't be too hard on those players. I will individually talk to them (encourage mostly, occasional demand more) and then give the others a kick up the arse.
Youngsters: It's the same with youngsters. I like to build them up and allow them to play without added pressure. If I have a youngster with good determination and a positive personality I may test the waters if he has a poor game by giving him a rocket but he would have to be playing really poor for this to happen (6.0 for instance). He would also have to have been generating poor match ratings for 2, 3 or maybe even 4 games for me to want to crack the whip.
Time in the job: I also like to take into account how long I've been in the job; my reputation and level of support from players. If I've just come through the door and the managerial support isn't great then I'd be wary of gobbing off at the players. It would disrupt things early on and possibly make my job harder.
Player personalities: Considering the hierachy and dynamics is another thing I take into account. For example in my previous job at AC Sparta Praha I was playing away against FK Teplice. According to the betting odds we were being touted as comfortable favourites. I noticed before the game that several players were complacent. I tried to rectify it with a stern pre-match team talk. We were winning 2-1 by the hour mark and playing reasonably well but still a few players were showing signs of complacency. We eventually won 3-1. I berated the team at full-time.
After the match, Bořek Dočkal (Team Leader & Icon) informed me that he wasn't happy with the team-talk and felt it was too harsh. I thought "here we go" I was ready to let him have it until I realised that 14 players agreed with him. Our relationship soon fell apart after that lol.
Now I have no idea if any of the things I like to do actually make that much of a difference or how long morale would stay low after games if I gave the team a verbal volley. It's just how I like to approach shouts and the fragile subject that is morale.