Recently, I ran into a note, 1226594. This note describes that in the account overview, the most recent activities are not shown. This is something we have noticed already from the start of the CRM Webclient. The logic to select the activities of a customer is basically selecting a set number of entries where the customer is mentioned.
On database level, this is done by selecting from CRMD_ORDER_INDEX up to X rows. The number of rows to be selected can be influenced in BADI CRM_BP_UIU_BT. In this BADI, you can also influence the selection as described here.
The biggest problem with the selection of the activities is that when the total number of the activities becomes bigger than the X (of the up to X rows), the system selects the first X (the oldest). This is due to the sorting of the CRMD_ORDER_INDEX table.
Note 1226594 implements a fix so that the latest activities are shown.
I strongly recommend you implement this note. The need for the implementation of BADI CRM_BP_UIU_BT as described here is now less relevant.
Of course, implementing for instance cv_max_hits = '10' in BADI method CHANGE_SELECTION of CRM_BP_UIU_BT will still improve performance.