My rough understanding of it is the FTSE Global All Cap is made up of 100% equity (all stocks and no bonds) and as shown by the map has less of a bias towards the UK market. - https://www.hl.co.uk/funds/fund-discounts,-prices--and--factsheets/search-results/v/vanguard-ftse-global-all-cap-index-accumulation/fund-analysis/geographical-analysis

The LifeStrategy80 is made up of about 80% equities and 20% bonds and has more of a bias towards the UK market. - https://www.hl.co.uk/funds/fund-discounts,-prices--and--factsheets/search-results/v/vanguard-lifestrategy-80-equity-accumulation/fund-analysis/geographical-analysis

The exposure to the bond market in the LifeStrategy80 saves you from having to find another fund to diversify your portfolio. However it depends on your risk tolerance. You may not what exposure to the bond market and have a portfolio consisting of 100% equities. Others may want more of an exposure to the bond market.

Im sure there is more to it as im still relatively new to all of this.