Even if you hold just one AIM buy trade amount of TLT (and gold), then whenever AIM does indicate a buy trade you might find for whatever reason the share price is down the value of TLT (or gold) may have risen and be a more appropriate choice of 'cash' to deploy into more shares.
If for instance cash deposits had risen 4%, but TLT had risen 10% then that 'cash' buys the additional stock at a relatively cheaper price.