Someone tripped over the mains cable into which the bass amp i was using on friday was plugged.
The D.I feed was coming directly from the amp as the FOH engineer couldn't find one that worked in time, so I lost the amp and the PA lost the DI out.
And it stayed out until the berk who fell over it, plugged it back in. it wasn't my amp and I had no idea where the mains cable was routed.
This was about 2 verses and a chorus.
If I had used a DI box BEFORE the amp,like I always do when engineering a band rather than playing bass, there would have been bass in the PA, and in my in ears, despite the amp going down.
So yes, a DI is an essential, inexpensive portable bit of kit that you need.