Is it worthwhile realising a capital loss on shares?

If a person holds shares that are worth a lot less now than they paid for them, is it worthwhile to do a 'bed and breakfast' deal to realise a capital loss?

I am suggesting this because they still hold the shares, so if they happen to appreciate again, there is no loss to them. The capital loss can be carried forward indefinitely until either these or some other share or asset is sold with a capital gain and the loss can be offset against it. The flexibility and availability of the capital loss seems to me to be a significant benefit at no real cost in our current circumstances, but maybe someone can spot a flaw in my suggestion?

I just don't see any point in your suggestion.

Say I bought 1,000 AIB at €18 and they are now worth €1. I have an unrealised loss of €17,000

If next year, I have a realised capital gain on Bank of Ireland, I can then sell sufficient shares in AIB to create a loss to match the gain.

There is no advantage in realising the loss first.

There is, in fact, a small disadvantage. You must use up your losses first before taking advantage of the anuual CGT exemption. So if your losses exceed your gains, you lose out on the CGT exemption.

You are needlessly incurring transaction costs as well.

You also face the small risk that the tax treatment may change and there might be some restriction placed on the use of losses.

The Revenue will allow notional losses on shares whereby on application to them, you create a notional loss to offset against real gains - however when you actually dispose of the shares in question - your original cost is replaced with the new value attirbuted to them to create the notional loss.

That would only apply when it is agreed there is no chance of the shares rising again. It wouldn't work for, say, BOI shares, unless they are nationalised. You can't opt for "negligible value" treatment just because your shares are lower in value than when you bought them.
There are also "bed and breakfast" restrictions, whereby if you sell off the shares, and crystallize the loss, then replace with identical shares within 4 weeks, that loss may only be carried forward and used against a gain made on the selling of those same shares.
Believe me, someone has been there before you spotting loopholes, and laws have been amended accordingly.