Originally Posted by
merziac
Yes, always, period.
For the exact reasons you list.
Randy's method is good, I have a different foolproof setup as well, PM if interested.
The method is good, but the spanner isn't - the two faces are tapered. The face against the cup can be tilted, especially if the washer is made to sit flat against the outer face; and it it's tilted, it can round the corners of the flats and/or slip off.
Best to use a proper BB cup spanner, they are not expensive - and keep the washer&bolt, you'll still need them.