As always this depends.
I routinely crop 1;1, 5:4 (or 4:3) and 2:1, as I feel comfortable with these shapes, and visualise this range of shapes when composing. I couldn't compose without some idea of the final crop, but equally understand why people like the freedom to custom crop at the processing stage, even though I prefer working to the constraints of fixed ratios. But it's not an unbreakable rule, just my default position.
I generally dislike the 3:2 ratio, especially for vertical images, yet it seems "right" for horizontal street type photography. Probably because I'm used to seeing lots of 35mm "no-crop" street photographs. I rarely use this ratio.
Some people choose fixed ratios so the prints fit into standard frame sizes, but as framed pictures are nearly always in a matt that can be cut to a custom aperture I've never fully understood that argument. Maybe some of the modern prints on metal etc only come as fixed sizes, or they mean standard pre-cut matt sizes.
With analogue, the print shape was sometimes dictated by the spurious subject matter at the edge, and one of the things I like about digital is that I can freely compose the image and clone out spurious edge details (if needed), which gives a more compositional control.
If it's a series of images, I prefer seeing them restricted to small range of consistent image ratios, or even only one; maybe that is too restrictive. I find it a bit disturbing if every image is a different ratio. The exception to this is a book where the design has actively used different image ratios as part of the overall design. Or, of course where the jarring of multiple image sizes has been deliberately used as part of the message.
With events, I can see why custom crops could be desirable, It's the quickest and cheapest way of getting focus on the subject.
An exception might be when a specific ratio is asked for. In the days when I did wedding photographs and we sent a "print' of the happy couple to the press, the published page(s) of wedding photographs were often a block of identically shaped and sized images., and I'm sure some of them specified the exact print size/format they required.
With events, If someone want's a print, would they not come back to you to ask for one? You could then rethink the crop and use other tools ( e.g. cloning) to make it a more standard size.
Or are you expecting your clients to print, or get printed, any files you have given them?. Do you offer prints as part of the service, and therefore expect clients fo come back to you? Have clients complained that prints cut off part of the image?
This has of course always been an issue, as back in the analogue days we tended to use 10 x 8 as our standard, but people would order, say a 7x5 prints which would often give us problems to print, as we had composed on the basis of a much "fatter" 10 x 8 ratio.
