Every ham radio operator should mail a QSL card for each QSO in the logbook, also if he don't collect himself no or anymore QSL cards.
The reason is simple: Perhaps your dialogue partner just begins to collect QSL cards as memory or for awards.
Here you can see my QSL cards, which are self-evident sended via bureau or direct to the dialogue partners.
On the left side you can scroll through the QSL cards of my home station and my activities inside Germany. On the right side you can scroll through the QSL cards of my DXpeditions so far.
Many of this QSL cards were printed by QSL-Shop. Because printing special QSL cards with minimum quantities of 500 or 1000 pieces is not economically for less than 50 QSO's. Therefore I have chosen for my smaller DXpeditions often postcards or photos with labels on it.
And since I am always busy sending QSL cards, I have now received many QSL cards through the QSL office - some also directly. I have therefore once reached into the boxes used for storage and scanned an unrepresentative selection. You can view the selection in 2 picture series with cards from DX stations here.
But since I am not only interested in QSOs to stations outside Europe, you can also see 2 series of pictures with QSL cards of some European stations here.