The pole offsets are in the order of hundreds of milli-arcseconds, whereas each second offset between UT1 and UTC produces an offset of (worst-case) ~14 arcseconds. Worlds of difference. Subtracting all leapseconds would yield an error of ~6 arcminutes, which can ruin your day if you are using any instrument with a small FoV (I know since I had that issue before where due to some hardware issues the telescope clock had lost a couple clock pulses and was 10-20s off compared to the observatory master clock).

They need to be backed out to linearly interpolate between entries to avoid a discontinuity.

Ah.. if you want to apply it on the day of the leapsecond. Fair. I meant more in general. As in all other cases you can just more or less blindly apply it.

In practice I can't say I have been bitten by UTC+leap second issues before nor have I even heard from observatories being bitten by this. Now GPS epoch rollover - that I have been personally experienced issues with.

In fact, bootstrapping from recent residuals suggests there is a reasonable chance of a positive leapsecond in the next several years. Each ordinary leapsecond causes substantial disruptions and system outages, and there has never been a positive leap second so it's reasonable to expect substantial issues.

We'll see if there will be a negative leapsecond in the future. But so far it also seems in line with no leapsecond at all.