This question has been asked in the forums many times, just in different formats. A more recent thread:
viewtopic.php?t=12915
Here's a thread with some useful quotes and comments:
viewtopic.php?t=4832
Another one:
https://www.skyscript.co.uk/forums/viewtopic.php?t=1037
I have been looking at Indian astrology more recently, and their rules tend to be more clear, IMO, although in practice I don't see it working as well in my own natal chart.
I follow the general rule that benefics behave as benefics but when ill dignified they become debilitated in the ways of their sign and placement. This doesn't necessarily mean they are "bad," but there is something out of the norm about them, which may lead to problems in the chart (whether it is a natal chart, event chart, horary, etc- it is universal). They can still perform in positive ways, but their ability to do so is lessened and/or they may cause harm, even possibly unintentionally. Generally, the harm is not of the magnitude of an ill dignified malefic in an accidentally strong house, etc. Maybe someone can show examples counter to that but I haven't seen it myself. Malefics when good can perform well but there are usually still some downsides and disappointments somehow. Malefics when badly placed are often very destructive when given power in the chart to allow that. I have seen this too many times throughout astrology to believe otherwise. In cases where they are somehow alleviated, this will certainly help, such as being received by a strong benefic, Venus or Jupiter for Mars or Jupiter for Saturn. If they are placed in houses where they are cadent and don't behold the ascendant or the ascendant lord in any aspect, then even though they have the potential to do harm, that harm might be reigned in more.