After improving all his cultivation methods Zhang Yi took much longer than before to strengthen his cultivation base, fortunately, he continued to double cultivate every day and thus was able to refine his qi several times and eliminate impurities.
His qi might not be as pure as before, but he knew it was impossible for him to go on forever without using cultivation resources even with his talent if he didn't want to take thousands of years to reach a higher realm.
So it was better to use cultivation resources at a time he needed than at a time when he was safe and just wanted to improve his cultivation faster, so he could feel the ease of using pills to improve his cultivation.