I think that your logic is faulty though - since the fund you are switching to will be up by exactly the same amount (barring a pullback in your favour ie accidental market timing) it makes no difference when you make the switch - fees are fees.
If you are interested in tracker funds and can cope with the limited selection (own funds only) the Vanguard platform is very good for fee dodging (and in the interest of long term holds - fees also compound over time).
Ah, I see what you mean. I guess it's just a psychological thing about locking in profit/loss.
Since I bought it, it has been yo-yoing around so my thinking is, sell on a peak and buy back on a dip and that way I get to swap for 'free' and also hopefully gain slightly more when it climbs again (as I originally bought on a peak).
There's probably some gamblers fallacy going on there but it makes sense in my head.
I already use Vanguard for my SIPP and I have a chunk of my S&S ISA in a LifeStrategy fund — this was an attempt to diversify a bit and not put all of my eggs in the Vanguard basket. Plus, the last time I checked, the UK LifeStrategy funds didn't have a huge weighting towards US stocks.
Ironically, since I bought the i-shares S&P500 tracker, my LifeStrategy fund has outperformed it significantly…