Posting the cap on the end of the barrel is perfectly safe; the pen comes to no harm. Over time a faint band of wear may appear on the precious resin where the cap sits. It is barely visible and can be polished out if it bothers you. In any case, wear tends to show up elsewhere first, at the threads and on the cap, simply from screwing it on and off so often.
The only real consideration is balance. On the larger models a posted cap shifts the centre of gravity noticeably backwards, which many people find uncomfortable. On the slimmer, lighter 144 this matters far less, and for large hands the pen is often simply too short unposted. So anyone wanting to use an inherited pen should not be put off. A fountain pen suffers far less from regular use than from lying untouched for years with dried ink in the feed.