Not least the compounding effect of long amortisation - it makes this year 'cheaper' but they're loading up the costs of future years as the costs will appear for years to come.
It's like taking a loan of 200 a month to buy a new car over 10 years, when you want a new one in 5 years time you are still paying out 200 a month for your old car before you take a new loan for another 200 a month - now its costing you 400 a month. If you're budget allows for 300 a month you can't afford it so have to get a cheaper car the second time.
Chelsea will presumably want to spend and spend every year, at some point they will run out of FFP wiggle room due to earlier years ongoing amortisation costs.
I suspect they are hoping for either big sales to offset, big increase in allowable loss figure, or scrapping of financial rules altogether in the 5 year time frame.